Some good at damaged stability

Discussion in 'Stability' started by fcfc, Jun 19, 2013.

  1. fcfc
    Joined: Feb 2005
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    fcfc Senior Member

  2. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Hey, we're pitching too much...Let's pump all the ballast to the ends to increase the moment of inertia to stop the pitching...

    (actual comment from a ship captian I once worked with)
     
  3. Crowsnest
    Joined: Jun 2012
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    Crowsnest Junior Member

    Jehardiman:
    Didn't you got scared sailing with that Cpt ?
    I've have a brieff look at the accident report. They are thinking as one of the possible causes, a wrong declaration of containers weights.
    Lord bless us ¡¡
    How wrong was that declaration ? Too wrong for being possible, I think.
    Im for the wrong stowage/calculation + speed explanation.

    Regards.
     
  4. rxcomposite
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    rxcomposite Senior Member

    In my book, the designers are advised to check very carefully the calculations on the use of forepeak ballast/water tanks. Says it could snap the boat in two even when the boat is lightly loaded.
     
  5. Crowsnest
    Joined: Jun 2012
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    Crowsnest Junior Member

    Heads ballast.

    Here are attached two load cases for a medium sized container ship.

    Case-1 Evenly loaded along the whole length. 2000 mT.
    Case-2 Evenly loaded along the whole length. 1000 mT. +
    + 500 mT at each head ballast tank.

    Even with this light loads, check values of maximum bending moments.
     

    Attached Files:

  6. Crowsnest
    Joined: Jun 2012
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    Crowsnest Junior Member

    Correction to pics.

    Those pics belong to a beta version of a program. I mistook It.

    Here are the same attachments got from the release one.

    Even load=5000mT
    Ballast head loads= 500 mT each.

    My apologizes.
     

    Attached Files:

  7. nettersheim
    Joined: Sep 2010
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    Location: France

    nettersheim Consultant

    Hello,

    According to on site pictures, the two broken parts of "MOL Comfort" at an early stage (let's say few hours after separation) look to float quite even keel.

    Initial stability and ... damage stability were satisfactory.

    This observation may indicate that no big mistake has been done either by the crew or by people in charge of preparing loading/stowage plan. Or if some mistake has been done, it has been in the minor range.

    Therefore the initial question is still on the table : why a recent vessel broke in two ?

    I am not sure we will have an answer one day : too much interests at play in this story ! Class ... Shipbuilder ... Rules ... use of high tensile steel ...

    Fortunately the crew has been saved, this time...
     
  8. El_Guero

    El_Guero Previous Member

    Did you get off at the next stop?
     
  9. dskira

    dskira Previous Member

    MOL Comfort.
    Right, not only the crew have separate quarters but also they have separate ships. That's Comfort for you :p
     
  10. Crowsnest
    Joined: Jun 2012
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    Crowsnest Junior Member

    Nettersheim:
    Good point the drafts one. I agree with you.
    I arrived to a similar conclussion from a simple "common sence" approach.
    Given the very big containers quantity, the probability for a located catastrophic overload due to cargo, at a section looks to be very low.
    Of course there are lots of interests playing around this accident. But as we are no part of any of them, in may oppinion we are free to think and say whatever we want.
    Hence, from my very modest oppinion Im more for the design or construction failure. May be a torsional stress more than a bending one.

    Regards
     

  11. nettersheim
    Joined: Sep 2010
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    nettersheim Consultant

    Thanks for your point , Crowsnet.

    I am always upset by the fact that master and officers are very often wrongly accused in such case.

    Just remember the bulk carrier "Derbyshire", among numerous other cases ... Class has accused the crew of many faults. In the end and after years and years of search for the wreck (funded by I.T.F) and legal procedure in Great Britain we have learnt that it was design, rules and therefore class who were guilty.

    In "MOL Comfort" case, as you point out we are likely facing a design problem (torsional stress, why not ?) combined with undue use of high tensile steel (brittle crack ?).

    Definitely not an intact and damage stability matter !
     
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